In this July 17, 2018, photograph, ramp workers prepare a Southwest Airlines Boeing 737 for departure to Denver from Minneapolis International Airport in Minneapolis. Southwest Airlines overcame rising fuel prices to top profit expectations, though an inflight disaster in which a passenger was killed had an adverse effect on revenue. Second-quarter earnings were $733 million, topping Wall Street expectations. (AP Photo/David Zalubowski) ORG XMIT: NYAG401(Photo: David Zalubowski, AP)

Southwest Airlines has had to remove an unusually high number of aircraft from service at the last minute this week, forcing the airline to declare an "operational emergency'' in a strongly worded memo to mechanics Friday.

The airline, which has been in prolonged and often contentious contract talks with its mechanics, ordered all hands on deck to get the planes back in the air. Mechanics who call in sick while the emergency status is in place will need a detailed doctor's note upon return, the memo says. Without it, they are subject to firing. Vacation requests and shift trades are also on hold unless already approved.

"This is not the type of communication I (or any leader) want to issue, but it is necessary to get our aircraft back in service in order to serve our customers,'' the memo from Lonnie Warren, senior director of technical operations, said.

The situation is not as ominous as it sounds for travelers – the airline plans for about 20 planes a day to be unexpectedly taken out of service, so a doubling would take that to 40 planes out of 750 in its fleet. So far, there have not been widespread flight cancellations as the long holiday weekend and February school vacations begin.

Southwest canceled 100 flights Friday, more than any U.S. carrier but still just 2 percent of its scheduled flights, according to flight tracker FlightAware. Some were due to fewer aircraft in service, Southwest spokeswoman Brandy King concedes, but the airline did not break out the number and said it has been trying to minimize the impact. Southwest has a weather alert in place in several cities and typically proactively cancels flights so passengers aren't stranded.

But it's the latest shot fired in a bitter contract dispute between Southwest and its mechanics, who are represented by the Aircraft Mechanics Fraternal Association. Contract negotiations have been ongoing for several years and currently involve a mediator. The key sticking point is Southwest's desire to outsource some maintenance.

The memo, first reported by the Chicago Business Journal, was sent to employees at Southwest's maintenance bases in Phoenix, Las Vegas, Orlando and Houston.

Such operations emergencies are often declared in the wake of high absenteeism. Another possible reason for more aircraft out of service, which has surfaced in other industry labor disputes: Mechanics are doing everything by the book, writing up more aircraft issues than usual, which slows down the operation.

Bret Oestreich, national director of the mechanics' union, disputed that notion, saying Southwest mechanics are working normal schedules and normal overtime. He said the airline has had higher numbers of FAA inspections following an CBS report of maintenance deficiencies.

He also said Southwest is short of aircraft because 22 planes were recently taken out of service for inspections of their engine “O rings.” (Southwest says inspections were completed and the aircraft were returned to service.)

Oestreich criticized Southwest for declaring the emergency.

"Unfortunately, Southwest’s response has been to increase the level of coercion and further degrade safety,'' he said in a message to members Friday.

He said that the "Southwest-created emergency'' will force mechanics who haven't had time to see a doctor to go to work sick and that potential mandatory overtime, another byproduct of the emergency status, will hurt mechanics with child-care obligations or fatigue from their regular shift.

"No matter how severe the provocation, AMFA asks its members not to be baited into acts of defiance that will be characterized as insubordination,'' Oestreich said in the memo. "We must follow the adage “work now, grieve later.”

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